I have a mix of differnet size, type and colour of pellet in mine.
If I'm fishing boilies (rare) then I usually crush one or two a bit and add that too.
Be aware that if you soak in oil like Mermaid does, the bag will take much monger to break down.
Stating the obvious, but as you are new to it...the cooler the water, the longer the PVA will take to break down. In fact in winter you may find a sizeable lump of PVA residue left on the hook i.e. never completely breaks down.
Also, you can use PVA nuggets for various things.
You can buy them in the tackle shop for 3 a bag, or get them from work for nothing like me [

] used as packing material.
I pinch them around the bend of the hook to avoid braided hooklengths from wrapping around the hook on the cast (rig dependant)
You can also use them for temporary bouyancy for the hook when fishing over silt or in choddy margins
Or you can nick a couple onto the hook, they will melt and float to the surface. You can then use them as a target to fire freebies at.
PVA is the future (or was it garlic bread?)